help diagnosing misfiring cylinder

My bet would be a clogged #4 pilot jet. I would also replace the spark plug caps.
Steve

I had something similar happen on my '78 650. I chased my tail for a long time, pretty well ready to just call it quits and walk away from it.

If you haven't had the carbs off for a good clean, do this. And make sure you REALLY clean them out well. I thought I had initially cleaned mine well after I picked the bike up, but found the same thing you did when you took the bowl off- there was a bit of dirt and particulate in the bowls. So I took everything off, and heavily soaked the carbs (all of them) in carb cleaner. Take all of your adjusting screws out (but make sure you note where you started) and soak all the passages. Take the floats off completely and remove any o-rings. Replace the o-rings if they seem worn, cracked, or rotting at all. These can also drop particulate into passageways. After things have soaked for a while, take compressed air and thoroughly blow out all of the passages. I was surprised at how much particulate came out of my carbs when I did this. It's easiest to do with a rubber air tip as it seals well against the opening. Blow air in both ways through the openings to fully dislodge anything. Soak the carbs again if you feel the need to and repeat the cleaning process.

Any small particulate can cause big issues with fueling like that. Especially if there's anything worked into the pilot air circuit. I know it can be a painful, tedious process to do a full clean, but give it a go. It sounds like this could be one of the last things to really check.

Good luck!

Also, I noticed again, that I am easily shocked when I ground myself with one hand and touch #4 at the bottom of the boot, right by the engine.

You should not get a shock when touching the plug cap or high tension lead. This would indicate the HT charge leaking via dirt or corrosion or crud or moisture and probably a poor or intermittent spark

My suggestion would be to take off the gas tank, wipe down the coil(s) and plug leads (HT leads) with a cloth. Spray the coils and wires with WD 40 and wipe again.
Remove the plug cap, cut 1/4 inch from the end of the plug lead and screw the plug cap back on or replace it altogether as Steve suggested as they do go bad. The resistors in the cap sometimes fail
Clean the plug cap and clean the ceramic part of the plug.

If you want to see how dirt in this area can cause misfire take a graphite pencil and draw a line the length of the spark plug ceramic

Good luck

aenikolopov wrote: I should add - adjusting the air screw all the way in and all the way out has no effect.

I agree with the other guys. That's potentially the smoking gun.

SWest wrote: My bet would be a clogged #4 pilot jet. I would also replace the spark plug caps.
Steve

Ding ding ding. Opened it up and the #4 pilot jet was completely clogged. Cleaned it out, and the cylinder fires!
I think I blew out half my Dyna S, but that's for another thread. Thanks everyone.